We hypothesize that a portion of the Marfan phenotype is caused by perturbation of TGFbeta activity. A potential mechanism is that loss of the molecular interaction between fibrillin-1 and LTBP results in activation of TGFbeta. Support for this hypothesis was obtained from the finding that fibrillin-1 hypomorphic mice display developmental defects in lung septation due to abnormal activation of TGFbeta (Neptune, et al., 2003). In order to test whether the molecular interaction between fibrillin-1 and LTBP is required for normal TGFbeta signaling and to determine whether loss of this interaction will result in activation of TGFbeta signaling, we propose in Specific Aim 1 to abolish binding of fibriUin-1 to LTBP both in vitro and in vivo. Analyses of mice in which a mutation in fibrillin-1 has been engineered to abolish binding to LTBP, compared to analyses of fibrillin-1 deficient mice, should allow us to directly determine whether this mechanism is responsible for the activated TGFbeta phenotype observed in the fibrillin-1 deficient lung and whether perturbation of TGFbeta signaling through this mechanism is responsible for Marfan-like phenotypes in any other tissues. The mice generated in Specific Aim 1 will be especially instructive because resulting phenotypes will indicate which tissues are most affected by the singular loss of the molecular interaction between fibrillin-1 and LTBP. In addition to dysregulated TGFbeta activity, perturbations of signaling by TGFbeta -related growth factors may play important roles in the pathogenesis of the Marfan syndrome. Since it is possible that the Marfan syndrome results from the effects of mutations in fibrillin-1 on multiple molecular interactions mediated by fibrillin-1, we propose in Specific Aim 2 to identify other TGFbeta-related growth factor family members that interact with fibrillin-1 and to determine whether any of the identified ligands are relevant to pathogenesis of the Marfan syndrome. To address the latter issue, we will determine the fates of selected BMPs, their receptors, and their downstream signals in fibrillin-1 null mice using immunohistochemical techniques. Results obtained from these investigations will inform and advance our programmatic goal of identifying novel targets for therapeutic intervention in the Marfan syndrome.